Over recent years, telephony networks have become more sophisticated and it has become possible for an increasing number of services to be provided, in addition to the fundamental provision of allowing a first customer Lo be connected to a second customer.
Telephony systems of this type are often referred to as intelligent networks, and provide such services as automatic call distribution, store and forward, fax to speech, call queuing, voice menu systems, call diversion, follow-on and voice prompts, etc.
Service nodes are units within the network where intelligent services are concentrated and made available to customers connected to the network via switching mechanisms provided within the network. At the node itself, a large switching device is provided which allows customer calls to be connected to peripheral devices under the control of central control processing means, such as a mini or mainframe computer. In known systems, it is necessary for the control computer to analyse signals generated by calling customers, in order that peripheral devices may be connected and, as necessary, disconnected etc. Thus, once a particular service has been established, this is generally driven under the control of a particular peripheral device. However, it is necessary for the central control computer to observe the operation of a connection between peripheral devices and external lines, in order to ensure that the integrity of the overall network is maintained.
A problem with known service nodes is that it is desirable to have large switches at the nodes, so that maximum benefit may be gained from a large number of shared services. However, as the number of shared services increases, with a resulting increase in the size of the connecting switch, the size and power of the control computer must also increase, along with the bandwidth of the communicating link between the computer and the switch.